The present invention relates to the finish for a cylinder liner, and in particular to chromium plated internal combustion engine cylinder liners, and to a method of applying this finish.
In the manufacture of chromium plated cylinder bores, the inner cylindrical walls are typically made porous in the range of 10%-50% by a variety of methods, such as reverse current etching, as disclosed, for example, in U.S. Pat. No. 2,314,604, No. 2,412,698, No. 2,430,750, No. 2,433,457, No. 2,620,296, chemical etching, or various mechanical methods. These methods provide virtually mirror smooth plateau bearing surfaces surrounding the pores or crevices formed thereby.
Due to variations inherent in any manufacturing process, the piston rings of the pistons which reciprocate in the cylinder bores and the inner cylindrical bearing surfaces of the bores often do not match, which is detrimental to obtaining a positive seal to high pressure gases or liquids. To cause the piston rings to lap in to fit the cylinder bore surface, it has been known in the past to provide an abrasive finish to the entire cylindrical wall of the cylinder liner by a dry abrasive blasting method, such as is disclosed in U.S. Pat. No. 3,063,763. As described in the aforementioned patent the break-in surface typically has a depth of porosity induced by blasting of from 7 to 20 microinches depending on the size of abrasive used in the blast. In this prior process, the representative coating is formed by blasting the surface of a typical 9" diameter by 22" cylinder with around 100 pounds of abrasive within about a minute. When using that amount of abrasive, each part of the surface is impacted by a large number of particles, resulting in a thoroughly roughened surface having sharp, closely spaced projections.
Disadvantages of the known cylinder liner break-in finish includes a relatively long "break-in" period during which the piston rings lap in to fit the cylinder bore, excessive ring wear and piston ring groove wear during the prolonged break-in period and an undesirably high oil consumption during this break-in period, as well as during subsequent operation of the engine as a result of increased residual porosity.
It is, therefore, an object of the invention to provide a finish to the inner cylindrical surface of a cylinder liner which results in a comparatively short break-in period relative to the known finishes, minimal ring and ring groove wear, and which will result in reduced lubricating oil consumption while still maintaining outstanding wear resistance.